U.S. Pat. No. 6,036,889 discloses a conductive thick film composition comprising a mixture of: a metallo-organic decomposition (MOD) compound; a first metal powder with a particle thickness of about 1 μm in an amount of about 1 to about 10 times the amount of the MOD compound by weight; and, an organic liquid vehicle in an amount of about 0.4 to 1.5 times the MOD compound by eight. Furthermore, U.S. Pat. No. 6,036,869 discloses at col. 9, lines 28–32, that the vehicle used in the composition dissolves the MOD compound and suspends the metallic constituents of the mixture to provide inks and pastes that can be applied by screen printing, stencil printing, gravure printing or any other direct contact printing processes.
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In direct thermal thermography a visible image pattern is formed by image-wise heating of a recording material.
In 1982, J. W. Shepard stated in J. Appl. Photographic Engineering Vol. 8, pages 210–212 reported that the catalyst in the thermal development of photothermographic and thermographic materials based on organic silver salts was very small silver particles. In 1989, A. T. Ram, J. L. McCrea and R. Snell stated in J. Imaging Technology volume 15, pages 169–177 that photolytic silver acts as a catalyst in the reduction of silver carboxylates by reducing agents. In 1989, D. H. Klosterboer stated in Imaging Processes and Materials, Neblette's 8th Edition, Edited by J. Sturge, V. Walworth and A. Shepp, Van Nostrand pages 279–291 that silver reduction can occur in all reactions from the silver filament in an autocatalytic reaction.
U.S. Pat. No. 5,051,335 discloses a process for forming an image which comprises imagewise exposing a heat developable light-sensitive material comprising light-sensitive silver halide emulsion layers on a paper support, and thereafter heating the same to develop the image, wherein at least one subbing layer comprising a hydrophilic binder and at least one material capable of inhibiting fog selected from a light-insensitive silver halide, colloidal silver, an organic silver salt, activated carbon powder and a porous silicon dioxide powder is interposed between the undermost layer among said light-sensitive silver halide emulsion layers and said paper support, whereby fog is inhibited.
Furthermore, in 1991, D. A. Morgan stated in the Handbook of Imaging Science, Edited by A. R. Diamond, Marcel Dekker, pages 43–60 that dry silver reactions do not go to completion. Analysis of thermographic and photothermographic materials subsequent to thermal development confirmed that residual organic silver salt and residual reducing agent were still present in regions in which the maximum is possible image density with the materials had been attained.
Incomplete reduction of the organic silver salt present in maximum density regions is undesirable for two reasons: it represents ineffective use of the organic silver salt present and hence additional ingredient costs and it leads to unnecessary potential image density instability due to the potential for further reaction, thereby requiring a higher concentration of image density stabilizers than would otherwise be the case.